Rubber compositions comprising a specific combination of a coupling agent and a hydrocarbon resin

ABSTRACT

A rubber composition is based on at least: a diene elastomer; a reinforcing inorganic filler; an agent for coupling the reinforcing inorganic filler with the diene elastomer, said coupling agent being an organofunctional silane comprising at least one oligomer of general formula (I), as described in the claims, bearing at least one blocked mercaptosilane unit and at least one mercaptosilane unit, a hydrocarbon-based resin predominantly composed of monomers chosen from the group consisting of cyclopentadiene, dicyclopentadiene, methylcyclopentadiene and mixtures thereof, and a crosslinking system. A semi-finished article and a tire may comprise at least one such rubber composition.

BACKGROUND

The invention relates to rubber compositions comprising at least oneinorganic reinforcing filler and a specific combination of ahydrocarbon-based resin and of an agent for coupling the inorganicfiller with the elastomer; these compositions notably being intended fortyres and more particularly for tyre treads.

Since fuel savings and the need to protect the environment have become apriority, it has proven necessary to produce tyres having a reducedrolling resistance, without adversely affecting the other properties ofthe tyre, in particular without reducing the wet grip.

However, it is well known to those skilled in the art that animprovement in one performance quality for tyres is often obtained atthe expense of its other performance qualities.

For example, one way of giving a tyre high wet grip is to use, for thetread, a rubber composition which has a good hysteretic potential.However, at the same time, this tread must have the lowest possiblecontribution to the rolling resistance to limit the rolling-relatedenergy losses; i.e. it must have the least possible hysteresis.

Improving the rolling resistance has been made possible by virtue of theuse of novel rubber compositions reinforced with inorganic fillers, inparticular specific silicas of the highly dispersible type, which arecapable of rivalling, from the reinforcing perspective, a conventionaltyre-grade carbon black, while offering these compositions a lowerhysteresis, which is synonymous with a lower rolling resistance. Thesespecific silicas of the highly dispersible type typically have a BETspecific surface area that is within a range extending from 100 to 250m²/g.

In order to facilitate the dispersion of the reinforcing inorganicfillers, it is known practice to use coupling agents, also known asbonding agents, which have the role of providing connections or bondsbetween the surface of the inorganic filler particles and the elastomerof the rubber compositions, while at the same time facilitating thedispersion of this inorganic filler within the elastomeric matrix.

It is recalled here that the term “coupling agent” (inorganicfiller/elastomer) should be understood as meaning, in a known manner, anagent that is capable of establishing a satisfactory bond, of chemicaland/or physical nature, between the inorganic filler and the dieneelastomer; such an at least difunctional coupling agent has, forexample, the simplified general formula “Y—W—X”, in which: Y representsa functional group (“Y” function) that is capable of bonding physicallyand/or chemically to the inorganic filler, such a bond being able to beestablished, for example, between a silicon atom of the coupling agentand the surface hydroxyl (OH) groups of the inorganic filler (forexample the surface silanols when it is silica); X represents afunctional group (“X” function) that is capable of bonding physicallyand/or chemically to the diene elastomer, for example via a sulfur atom;W represents a divalent group for connecting Y and X. The couplingagents should in particular not be confused with simple inorganic fillercovering agents which, in a known manner, may include the Y functionwhich is active towards the reinforcing inorganic filler but which donot contain the X function which is active towards the diene elastomer.

Among the many existing filler/elastomer coupling agents,mercaptosilanes prove to be particularly advantageous. However, giventheir very high reactivity, blocked mercaptosilanes are generally used.It is recalled here that blocked mercaptosilanes, in a manner well knownto those skilled in the art, are silane precursors that are capable offorming mercaptosilanes during the preparation of rubber compositions(see, for example, US 2002/0115767 A1 or international patentapplication WO 02/48256). These molecules have a blocking group insteadof the hydrogen atom of the corresponding mercaptosilane. The blockedmercaptosilanes are capable of being deblocked by replacing the blockinggroup with a hydrogen atom, during the compounding and curing, to leadto the formation of a more reactive mercaptosilane, defined as a silanewhose molecular structure contains at least one thiol (—SH) (mercapto-)group bonded to a carbon atom and at least one silicon atom. Theseblocked mercaptosilane coupling agents are thus generally used in thepresence of a blocked mercaptosilane activator, the role of which is toinitiate, accelerate or amplify the activity of the blockedmercaptosilane, as is notably specified in U.S. Pat. No. 7,122,590. Suchan activator or “deblocking agent” for tyre rubber compositions isgenerally composed of a guanidine, in particular N,N′-diphenylguanidine(DPG).

Although it has been shown that the use of blocked mercaptosilanecoupling agents has the advantage of improving the rolling resistancewhen they are used in rubber compositions, they have the drawback ofdeteriorating the wet grip.

It is known that the wet grip performance of rubber compositions can beimproved by adding plasticizing hydrocarbon-based resins.

For example, EP 2338698 A1 describes a rubber composition comprising anelastomer, silica and a combination of a coupling agent comprising bothmercaptosilane groups and blocked mercaptosilane groups and of a resinof α-methylstyrene and styrene. It is found that some of the illustratedrubber compositions have degraded rolling resistance.

Thus, there is still a need to improve the rolling resistanceperformance for rubber compositions, notably those intended for tyres,without penalizing the wet grip performance.

The aim of the present invention is to meet this need.

SUMMARY

The Applicant has discovered, surprisingly, that a specific combinationof a coupling agent and of a hydrocarbon-based resin in a reinforcedrubber composition meets this need. Specifically, rubber compositionscomprising this specific combination have improved rolling resistancewhen compared with the compositions of the prior art, without the wetgrip being penalized. The compositions of the invention also have theadvantage of having improved grip performance on snow-covered ground.

Consequently, a first subject of the present invention relates to arubber composition based on at least:

-   -   a diene elastomer;    -   a reinforcing inorganic filler;    -   an agent for coupling the reinforcing inorganic filler with the        diene elastomer, said coupling agent being an organofunctional        silane comprising at least one oligomer bearing at least one        blocked mercaptosilane unit and at least one mercaptosilane        unit, the oligomer corresponding to general formula (I) below:        (A)_(p)(B)_(q)   (I)    -   in which        -   A is a symbol representing a blocked mercaptosilane unit            corresponding to general formula (II):

-   -   -   B is a symbol representing a mercaptosilane unit            corresponding to general formula (III)

-   -   -   in which formulae (II) and (III):            -   R₃ represents a group chosen from a hydrogen atom, a                linear or branched C1-C18 alkyl and a linear or branched                C2-C18 alkenyl,            -   each R₄, which may be identical or different, represents                a saturated, linear or branched C1-C6 divalent                hydrocarbon-based group,            -   each Z^(b) forms a bridging structure between a silicon                atom of one unit and a silicon atom of another unit,                these units possibly being identical or different, and                is chosen from the group consisting of (—O—)_(0.5) and                [—O(R⁰CR⁰)_(f)O—]_(0.5) with R⁰, which may be identical                or different, representing a group chosen from a                hydrogen atom, methyl, ethyl and propyl and f                representing a number within a range extending from 2 to                15,            -   each Z^(c), which may be identical or different, forms a                cyclic structure with the silicon atom of one unit and                is [—O(R⁰CR⁰)_(f)O—]_(0.5) with R⁰ and f as defined                previously,            -   each X, which may be identical or different, is chosen                from the group consisting of a hydrogen atom, a hydroxyl                group, a C1-C6 alkyl group, a C1-C6 alkoxy group and a                group) HO(R⁰CR⁰)_(f)O— with R⁰ and f as defined                previously,            -   with u+v+2w=3 in which u is a number equal to 0, 1, 2 or                3, v is a number equal to 1, 2 or 3 and w is a number                equal to 0 or 1,        -   p is a number within a range extending from 1 to 20,        -   q is a number within a range extending from 1 to 20, and

    -   a hydrocarbon-based resin predominantly composed of monomers        chosen from the group consisting of cyclopentadiene,        dicyclopentadiene, methylcyclopentadiene and mixtures thereof,        and

    -   a crosslinking system.

A second subject of the present invention relates to a semi-finishedarticle for a tyre, comprising at least one composition as definedabove. More preferentially, this semi-finished article for a tyre is atread.

A third subject of the present invention relates to a tyre comprising atleast one composition as defined above.

1—MEASURING METHODS USED

1.1—Measurement of the Glass Transition Temperature Tg

All the glass transition temperature Tg values are measured in a knownmanner by DSC (Differential Scanning calorimetry) according to thestandard ASTM D3418 (1999).

1.2—Measurement of the Softening Point of the Resins

The softening point of a resin is measured according to the standard ISO4625 (ring and ball method).

1.3—Measurement of the Mn, Mw and PI of the Hydrocarbon-Based Resins

The macrostructure (Mw, Mn, PI and Mz) of the hydrocarbon-based resin isdetermined by size exclusion chromatography (SEC) on the basis of thestandards ISO 16014 (Determination of average molecular mass andmolecular mass distribution of polymers using size exclusionchromatography), ASTM D5296 (Molecular Weight Averages and molecularweight distribution of polystyrene by High performance size exclusionchromatography) and DIN 55672 (size exclusion chromatography).

For these measurements, the resin sample is dissolved inantioxidant-free tetrahydrofuran up to a concentration of 1.5 g/l. Thesolution is filtered with a Teflon filter with a porosity of 0.45 μm,using for example a disposable syringe fitted with a filter. A volume of100 μl is injected through a set of size exclusion chromatographycolumns. The mobile phase is eluted with a flow rate of 1 ml/min. Thecolumns are thermostatically maintained at 35° C. in an oven. Detectionis performed by a refractometer thermostatically maintained at 35° C.The stationary phase of the columns is based on apolystyrene/divinylbenzene gel having a controlled porosity. The polymerchains are separated according to the volume that they occupy when theyare dissolved in the solvent: the larger the volume they occupy, theless the pores of the columns are accessible to them and the shortertheir elution time.

A Moore calibration curve connecting the logarithm of the molar mass(log M) to the elution time (et) is produced beforehand with polystyrenestandards and modelled by a third degree polynomial: log(molar mass ofpolystyrene)=a+b et+c et2+d et3.

For the calibration curve, polystyrene standards with narrow moleculardistributions are used (polydispersity index, PI, of less than or equalto 1.1). The range of molar masses of these standards extends from 160to about 70 000 g/mol. These standards may be grouped together in“families” of 4 or 5 standards having a log M increment of about 0.55between each family.

Use may be made of certified (ISO 13885 and DIN 55672) standard kits,for instance the kits of vials from the company PSS (Polymer StandardsService, reference PSS-pskitrll-3), and also an additional PS standardwith Mp=162 g/mol (Interchim, reference 178952). These kits are providedin the form of three vials each containing a family of polystyrenestandards in suitable amounts:

-   -   Black vial: Mp=1220, 4850, 15 500 and 67 500 g/mol,    -   Blue vial: Mp=376, 3470, 10 400, 46 000 g/mol,    -   Yellow vial: Mp=266, 1920, 7200, 28 000 g/mol,    -   PS162: Mp=162 g/mol.

The number-average molar mass (Mn), the weight-average molar mass (Mw),the average mass (Mz) and the polydispersity (PI) of the resin analysedare calculated from this calibration curve. This is why they arereferred to as molar masses relative to a polystyrene calibration.

For the calculation of the average masses and of the polydispersityindex, the limits of integration of the elution of the product aredefined on the chromatogram corresponding to the injection of thesample. The refractometric signal defined between the two limits ofintegration is “cut” every second. For each of the “elementary cuts”,the elution time ti and the area of the signal from the detector Ai areread off.

It is recalled here that: PI=Mw/Mn, with Mw the weight-average molecularmass and Mn the number-average molecular mass. It is also recalled thatthe masses Mw, Mn and Mz are average masses calculated according to thefollowing formulae:

${Mz} = \frac{\Sigma\mspace{14mu}{Ai} \times {Mi}^{2}}{\Sigma\mspace{14mu}{Ai} \times {Mi}}$${Mn} = \frac{\Sigma\mspace{14mu}{Ai}}{\Sigma\frac{Ai}{Mi}}$${Mw} = \frac{\Sigma\mspace{14mu}{Ai} \times {Mi}}{\Sigma\mspace{14mu}{Ai}}$in which Ai is the amplitude of the signal from the refractometricdetector corresponding to the mass Mi and to the elution time ti.

The equipment used for the SEC measurement is a liquid chromatographysystem, for example the Waters Alliance 2690 system comprising a pump, adegasser and an injector; a differential refractometer (for example theWaters 2410 refractometer), software for data acquisition andprocessing, for example the Waters Empower software, a column oven, forexample the Waters “Column Heater Module”, and four columns mounted inseries in the following order:

Molar Reference, mass Inside Particle for range Length diameter sizeTrade information Number Brand (g/mol) (mm) (nm) (μm) name purposesColumns 1 Polymer 200-400000 300 7.5 5 MIXED-D PL1110-6504 and 2Laboratories Columns 3 Polymer 200-30000  300 7.5 3 MIXLD-E PL1110-6300and 4 Laboratories1.4—Measurement of the Proton Content in a Resin

The aromatic proton content and the ethylenic proton content aremeasured by ¹H NMR. This determination is performed with respect to allof the signals detected. Thus, the results obtained are expressed aspercentage of the peak area.

The samples are dissolved in deuterated chloroform (CDCl₃) in aproportion of about 10 mg of resin in about 1 mL of solvent. The spectraare acquired on a Brüker Avance 500 MHz spectrometer equipped with aBrüker “broad band” BBO z-grad 5 mm probe. The ¹H NMR experiment uses asingle 30° pulse sequence and a repetition delay of 5 seconds betweeneach acquisition. 64 accumulations are performed at room temperature.The chemical shifts are calibrated relative to the protonated impurityof the deuterated chloroform; δ ppm ¹H at 7.20 ppm. The ¹H NMR signalsof the aromatic protons are located between 8.5 ppm and 6.2 ppm. Theethylenic protons, for their part, give rise to signals between 6.2 ppmand 4.5 ppm. Finally, the signals corresponding to the aliphatic protonsare located between 4.5 ppm and 0 ppm. The areas of each category ofprotons are taken relative to the sum of these areas to thus give anarea distribution percentage for each category of protons.

1.5—Measurement of the BET Specific Surface Area and of the CTABSpecific Surface Area

The BET specific surface area is determined by gas adsorption using theBrunauer-Emmett-Teller method described in “The Journal of the AmericanChemical Society”, (Vol. 60, page 309, February 1938), and morespecifically according to a method derived from the standard NF ISO5794-1, appendix E, of June 2010 [multipoint (5 point) volumetricmethod—gas: nitrogen—degassing under vacuum: one hour at 160°C.—relative pressure range p/po: 0.05 to 0.2].

The CTAB specific surface area values were determined according to thestandard NF ISO 5794-1, appendix G of June 2010. The process is based onthe adsorption of CTAB (N-hexadecyl-N,N,N-trimethylammonium bromide)onto the “outer” surface of the reinforcing filler.

1.6—Determination of the Microstructure of the Elastomers byNear-Infrared (NIR) Spectroscopy

Near-infrared (NIR) spectroscopy is used to quantitatively determine themass content of styrene in the elastomer and also its microstructure(relative distribution of the 1,2-, trans-1,4- and cis-1,4-butadieneunits). The principle of the method is based on the Beer-Lambert lawgeneralized for a multicomponent system. As the method is indirect, itinvolves a multivariate calibration [Vilmin, F., Dussap, C. and Coste,N., Applied Spectroscopy, 2006, 60, 619-29] performed using standardelastomers having a composition determined by ¹³C NMR. The styrenecontent and the microstructure are then calculated from the NIR spectrumof an elastomer film about 730 μm thick. The spectrum is acquired intransmission mode between 4000 and 6200 cm⁻¹ with a resolution of 2 cm⁻¹using a Brüker Tensor 37 Fourier-transform near-infrared spectrometerequipped with an InGaAs detector cooled by the Peltier effect.

1.7—Dynamic Properties of the Rubber Compositions (after Curing)

The dynamic properties are measured on a viscosity analyser (MetravibVA4000) according to the standard ASTM D 5992-96. The response of asample of crosslinked composition (cylindrical specimen 4 mm thick andwith a cross section of 400 mm²), subjected to a simple alternatingsinusoidal shear stress, at a frequency of 10 Hz, during a temperaturesweep, at a set stress of 0.7 MPa, is recorded, and the values of G* andtan 6 observed at −20° C. (i.e. G*_(−20° C.) and tan(δ)_(−2° C.)) arerecorded.

The same sample is also subjected, at a temperature of 23° C., to astrain amplitude sweep from 0.1% to 50% (forward cycle) and then from50% to 0.1% (return cycle). For the return cycle, the maximum value ofthe loss factor, denoted tan(δ)max, is recorded.

The tan(δ)_(max) results at 23° C. are indicated in base 100 and areobtained in the following manner: the tan(δ)_(max) result at 23° C.obtained for a test sample is calculated in base 100, the arbitraryvalue 100 being assigned to the control:tan(δ)_(max) result at 23° C. (base 100)=(tan(δ)max value at 23° C. ofthe test sample×100)/(tan(δ)max value at 23° C. of the control).In this way, a result less than 100 indicates a decrease in thehysteresis (which is favourable to the rolling resistance).

It is recalled that, as is known to those skilled in the art, the tan(δ)value observed at −20° C. is representative of the wet grip potential;the greater the tan(δ)_(−20° C.) value, the better the grip. The resultis expressed in base 100 by means of the following calculation: Anarbitrary value 100 is given to a control composition, a result greaterthan 100 indicating an increase in the tan(δ)_(−20° C.) value, thereforecorresponding to an improvement in the wet grip performance.tan(δ)_(−20° C.) result (base 100)=(tan(δ)_(−20° C.) value of the testsample×100)/(tan(δ)_(−20° C.) value of the control).

The G*_(−20° C.) results are indicated in base 100 and are obtained inthe following manner: the G*_(−20° C.) result obtained for a test sampleis calculated in base 100, the arbitrary value 100 being assigned to thecontrol:G* _(−20° C.) result (base 100)=(G* _(−20° C.) value of the testsample×100)/(G* _(−20° C.) value of the control).

In this way, a result less than 100 indicates a decrease in theG*_(−20° C.) (which is favourable to the grip on snow-covered ground).

2—DETAILED DESCRIPTION OF THE INVENTION

The invention and the advantages thereof will be readily understood inthe light of the description and the implementation examples.

A first subject of the present invention relates to a rubber compositionbased on at least:

-   -   a diene elastomer;    -   a reinforcing inorganic filler;    -   an agent for coupling the reinforcing inorganic filler with the        diene elastomer, said coupling agent being an organofunctional        silane comprising at least one oligomer bearing at least one        blocked mercaptosilane unit and at least one mercaptosilane        unit, the oligomer corresponding to general formula (I) below:        (A)_(p)(B)_(q)   (I)    -   in which        -   A is a symbol representing a blocked mercaptosilane unit            corresponding to general formula (II):

-   -   -   B is a symbol representing a mercaptosilane unit            corresponding to general formula (III)

-   -   -   in which formulae (II) and (III):            -   R₃ represents a group chosen from a hydrogen atom, a                linear or branched C1-C18 alkyl and a linear or branched                C2-C18 alkenyl,            -   each R₄, which may be identical or different, represents                a saturated, linear or branched C1-C6 divalent                hydrocarbon-based group,            -   each Z^(b) forms a bridging structure between a silicon                atom of one unit and a silicon atom of another unit,                these units possibly being identical or different, and                is chosen from the group consisting of (—O—)_(0.5) and                [—O(R⁰CR⁰)_(f)O—]_(0.5) with R⁰, which may be identical                or different, representing a group chosen from a                hydrogen atom, methyl, ethyl and propyl and f                representing a number within a range extending from 2 to                15,            -   each Z^(c), which may be identical or different, forms a                cyclic structure with the silicon atom of one unit and                is [—O(R⁰CR⁰)_(f)O—]_(0.5) with R⁰ and f as defined                previously,            -   each X, which may be identical or different, is chosen                from the group consisting of a hydrogen atom, a hydroxyl                group, a C1-C6 alkyl group, a C1-C6 alkoxy group and a                group) HO(R⁰CR⁰)_(f)O— with R⁰ and f as defined                previously,            -   with u+v+2w=3 in which u is a number equal to 0, 1, 2 or                3, v is a number equal to 1, 2 or 3 and w is a number                equal to 0 or 1,        -   p is a number within a range extending from 1 to 20,        -   q is a number within a range extending from 1 to 20, and

    -   a hydrocarbon-based resin predominantly composed of monomers        chosen from the group consisting of cyclopentadiene,        dicyclopentadiene, methylcyclopentadiene and mixtures thereof,        and

    -   a crosslinking system.

The term “composition based on” should be understood as meaning acomposition including the mixture and/or the in situ reaction product ofthe various constituents used, some of these constituents being capableof reacting and/or being intended to react with each other, at least inpart, during the various phases of manufacture of the composition.

In the present description, unless expressly indicated otherwise, allthe percentages (%) shown are mass percentages.

Furthermore, any range of values denoted by the expression “between aand b” represents the range of values extending from more than “a” toless than “b” (i.e. limits a and b excluded), while any range of valuesdenoted by the expression “from a to b” means the range of valuesextending from “a” up to “b” (i.e. including the strict limits a and b).

In the present patent application, the term “phr” means parts by weightof a constituent per hundred parts by weight of elastomer.

In the context of the invention, the carbon-based products mentioned inthe description may be of fossil or biosourced origin. In the lattercase, they may be partially or totally derived from biomass or may beobtained from renewable starting materials derived from biomass.Polymers, plasticizers, fillers and the like are notably concerned.

2.1—Constituents of the Rubber Composition

Diene Elastomer

As mentioned previously, the compositions in accordance with theinvention comprise at least one diene elastomer.

It is recalled here that the term “elastomer” (or “rubber”, the twoterms being regarded as synonymous) of the “diene” type should beunderstood, in a known manner, as meaning an (one or more is understood)elastomer at least partly derived (i.e., a homopolymer or a copolymer)from diene monomer(s) (i.e. monomer(s) bearing two conjugated ornon-conjugated carbon-carbon double bonds).

Diene elastomers may be classified in two categories: “essentiallyunsaturated” or “essentially saturated”. The term “essentiallyunsaturated” generally refers to a diene elastomer resulting at least inpart from conjugated diene monomers having a molar content of units ofdiene origin (conjugated dienes) which is greater than 15% (mol %);thus, diene elastomers such as butyl rubbers or copolymers of dienes andof α-olefins of EPDM type do not fall under the preceding definition andmay notably be termed “essentially saturated” diene elastomers (low orvery low molar content, always less than 15% (mol %), of units of dieneorigin). In the category of “essentially unsaturated” diene elastomers,the term “highly unsaturated” diene elastomer in particular refers to adiene elastomer having a molar content of units of diene origin(conjugated dienes) which is greater than 50% (mol %).

Given these definitions, the term “diene elastomer that is capable ofbeing used in the rubber compositions in accordance with the invention”more particularly refers to:

-   -   (a) any homopolymer obtained by polymerization of a conjugated        diene monomer containing from 4 to 12 carbon atoms;    -   (b) any copolymer obtained by copolymerization of one or more        conjugated dienes with each other or with one or more        vinylaromatic compounds containing from 8 to 20 carbon atoms;    -   (c) a ternary copolymer obtained by copolymerization of ethylene        and of an α-olefin containing from 3 to 6 carbon atoms with a        non-conjugated diene monomer containing from 6 to 12 carbon        atoms, for instance the elastomers obtained from ethylene and        propylene with a non-conjugated diene monomer of the        abovementioned type, notably such as 1,4-hexadiene,        ethylidenenorbornene or dicyclopentadiene;    -   (d) a copolymer of isobutene and of isoprene (butyl rubber) and        also the halogenated versions, in particular chlorinated or        brominated versions, of this type of copolymer.

Although it applies to any type of elastomer, notably diene elastomer, aperson skilled in the art will understand that the present invention ispreferably performed with essentially unsaturated diene elastomers, inparticular of the type (a) or (b) above.

In the case of copolymers (b), they may contain from 20% to 99% byweight of diene units and from 1% to 80% by weight of vinylaromaticunits.

The following are notably suitable as conjugated dienes: 1,3-butadiene,2-methyl-1,3-butadiene, 2,3-di(C₁-C₅ alkyl)-1,3-butadienes, for instance2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene,2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-isopropyl-1,3-butadiene, anaryl-1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene.

The following, for example, are suitable as vinylaromatic compounds:styrene, ortho-, meta- or para-methylstyrene, the “vinyltoluene”commercial mixture, para-(tert-butyl)styrene, methoxystyrenes,chlorostyrenes, vinylmesitylene, divinylbenzene or vinylnaphthalene.

Preferentially, the diene elastomer(s) of the composition according tothe invention may be chosen from the group of diene elastomersconsisting of polybutadienes (abbreviated to BRs), syntheticpolyisoprenes (abbreviated to IRs), natural rubber (abbreviated to NR),butadiene copolymers, isoprene copolymers and the mixtures of theseelastomers.

Such copolymers are more preferentially chosen from the group consistingof butadiene/styrene copolymers (abbreviated to SBRs), whether thelatter are prepared by emulsion polymerization (ESBR) or solutionpolymerization (SSBR), isoprene/butadiene copolymers (abbreviated toBIRs), isoprene/styrene copolymers (abbreviated to SIRs) andisoprene/butadiene/styrene copolymers (abbreviated to SBIRs).

More preferentially, the diene elastomer(s) of the composition accordingto the invention may be chosen from the group of diene elastomersconsisting of polybutadienes, butadiene-styrene copolymers,isoprene-butadiene copolymers, isoprene-styrene copolymers,isoprene-butadiene-styrene copolymers, and mixtures of these elastomers.

The elastomers may have any microstructure, which depends on thepolymerization conditions used, notably on the presence or absence of amodifying and/or randomizing agent and on the amounts of modifyingand/or randomizing agent used. These elastomers may, for example, beblock, random, sequential or microsequential elastomers and may beprepared in dispersion or in solution; they may be coupled and/orstar-branched or else functionalized with a coupling and/orstar-branching or functionalization agent.

According to a preferred embodiment, the elastomer is a functionalizeddiene elastomer.

Preferably, the functionalized diene elastomer is chosen from the groupof diene elastomers consisting of polybutadienes, syntheticpolyisoprenes, butadiene copolymers, isoprene copolymers, and mixturesof these elastomers. Even more preferentially, the functionalizedelastomer is a butadiene-styrene copolymer.

Preferably, the functionalized diene elastomer has a glass transitiontemperature Tg of less than or equal to −40° C., preferably within arange extending from −110° C. to −40° C., more preferentially from −110°C. to −60° C., even more preferentially from −110° C. to −80° C.

The term “functionalized diene elastomer” refers to a synthetic dieneelastomer which includes at least one chemical group comprising one ormore heteroatoms, for instance a sulfur atom S, a nitrogen atom N, anoxygen atom O, a silicon atom Si or a tin atom Sn. In the context of thepresent description, this chemical group is also referred to as“function”. The two terms are used without distinction.

This chemical group may be located at the chain end, that is to say atone end of the linear main elastomer chain. It will then be said thatthe diene elastomer is functionalized “at the chain end”. It isgenerally an elastomer obtained by reaction of a living elastomer with afunctionalization agent, that is to say any at least monofunctionalmolecule, the function being any type of chemical group known to thoseskilled in the art to react with a living chain end.

This chemical group may be located in the linear main elastomer chain.It will then be said that the diene elastomer is coupled or elsefunctionalized “in the middle of the chain”, as opposed to the position“at the chain end” and although the group is not located precisely atthe middle of the elastomer chain. It is generally an elastomer obtainedby reaction of two chains of the living elastomer with a coupling agent,that is to say any at least difunctional molecule, the function beingany type of chemical group known to those skilled in the art to reactwith a living chain end.

This group may be central, to which n elastomer chains (n>2) are bonded,forming a star-branched structure of the elastomer. It will then be saidthat the diene elastomer is star-branched. It is generally an elastomerobtained by reaction of n chains of the living elastomer with astar-branching agent, that is to say any polyfunctional molecule, thefunction being any type of chemical group known to those skilled in theart to react with a living chain end.

A person skilled in the art will understand that a functionalizationreaction with an agent comprising more than one function which isreactive with regard to the living elastomer results in a mixture ofspecies functionalized at the chain end and in the middle of the chain,constituting the linear chains of the functionalized diene elastomer,and also, where appropriate, star-branched species. Depending on theoperating conditions, mainly the mole ratio of the functionalizationagent to the living chains, certain species are predominant in themixture.

Preferentially, the functionalized diene elastomer comprises at leastone polar function comprising at least one oxygen atom.

Preferentially, the polar function may be chosen from the groupconsisting of silanol, alkoxysilanes, alkoxysilanes bearing an aminegroup, epoxide, ethers, esters, carboxylic acids and hydroxyl. The polarfunction notably improves the interaction between the reinforcinginorganic filler and the elastomer. Such functionalized elastomers areknown per se and are described notably in the following documents:FR2740778, U.S. Pat. No. 6,013,718, WO2008/141702, FR2765882,WO01/92402, WO2004/09686, EP1127909, U.S. Pat. No. 6,503,973,WO2009/000750 and WO 2009/000752.

In a preferred embodiment, the functionalized diene elastomer is a dieneelastomer including a polar function that is a silanol.

Preferably, the functionalized diene elastomer comprises, at one end ofits main chain, a silanol function or a polysiloxane group bearing asilanol end of formula —(SiR₁R₂—O—)_(m)H with m representing an integerranging from 3 to 8, preferably 3, R₁ and R₂, which may be identical ordifferent, represent an alkyl radical of 1 to 10 carbon atoms,preferably an alkyl radical containing 1 to 4 carbon atoms.

This type of elastomer may be obtained according to the processesdescribed in EP 0778311 and more particularly according to the processconsisting, after a step of anionic polymerization, in functionalizingthe living elastomer with a functionalization agent of cyclicpolysiloxane type, as long as the reaction medium does not allow thepolymerization of the cyclopolysiloxane. Cyclic polysiloxanes that maybe mentioned include those corresponding to formula (VII):

where m represents an integer ranging from 3 to 8, preferably 3, and R₁and R₂, which may be identical or different, represent an alkyl radicalof 1 to 10 carbon atoms, preferably an alkyl radical containing 1 to 4carbon atoms. Among these compounds, mention may be made ofhexamethylcyclotrisiloxane.

In another preferred embodiment of the invention, the functionalizeddiene elastomer includes a polar function which is an alkoxysilaneoptionally bearing another function (or bearing another chemical group,these expressions being synonymous).

Preferably, this functionalized diene elastomer comprises in its mainchain at least one alkoxysilane group bonded to the elastomer chain viathe silicon atom, and optionally bearing at least one other function.

According to certain preferred variants, the alkoxysilane group(optionally bearing another function) is located at one end of the mainchain of the elastomer.

According to other preferred variants, the alkoxysilane group(optionally bearing another function) is located in the main elastomerchain. The silicon atom of this function bonds the two branches of themain chain of the diene elastomer.

The alkoxysilane group (optionally bearing another function) comprises aC₁-C₁₀ alkoxy radical, optionally partially or totally hydrolysed tohydroxyl, or even a C₁-C₈, preferably C₁-C₄ alkoxy radical, and is morepreferentially methoxy and ethoxy.

The other function is preferably borne by the silicon of thealkoxysilane group, directly or via a spacer group, defined as being asaturated or unsaturated, cyclic or non-cyclic, divalent, linear orbranched, aliphatic C₁-C₁₈ hydrocarbon-based radical, or a divalentaromatic C6-C₁₈ hydrocarbon-based radical.

The other function is preferably a function comprising at least oneheteroatom chosen from N, S, O or P. Mention may be made, by way ofexample, among these functions, of cyclic or non-cyclic primary,secondary or tertiary amines, isocyanates, imines, cyanos, thiols,carboxylates, epoxides or primary, secondary or tertiary phosphines.

Mention may thus be made, as secondary or tertiary amine function, ofamines substituted with C₁-C₁₀ alkyl, preferably C₁-C₄ alkyl, radicals,more preferentially a methyl or ethyl radical, or else of cyclic aminesforming a heterocycle containing a nitrogen atom and at least one carbonatom, preferably from 2 to 6 carbon atoms. For example, methylamino-,dimethylamino-, ethylamino-, diethylamino-, propylamino-,dipropylamino-, butylamino-, dibutylamino-, pentylamino-,dipentylamino-, hexylamino-, dihexylamino- or hexamethyleneamino-groups,preferably diethylamino- and dimethylamino-groups, are suitable.

Mention may be made, as imine function, of ketimines. For example,(1,3-dimethylbutylidene)amino-, (ethylidene)amino-,(1-methylpropylidene)amino-, (4-N,N-dimethylaminobenzylidene)amino-,(cyclohexylidene)amino-, dihydroimidazole and imidazole groups aresuitable.

Mention may thus be made, as carboxylate function, of acrylates ormethacrylates. Such a function is preferably a methacrylate.

Mention may be made, as epoxide function, of epoxy or glycidyloxygroups.

Mention may be made, as secondary or tertiary phosphine function, ofphosphines substituted with C₁-C₁₀ alkyl, preferably C₁-C₄ alkyl,radicals, more preferentially a methyl or ethyl radical, or elsediphenylphosphine. For example, methylphosphino-, dimethylphosphino-,ethylphosphino-, diethylphosphino, ethylmethylphosphino- anddiphenylphosphino-groups are suitable.

Preferentially, the other function is preferably a tertiary amine, morepreferentially a diethylamino- or dimethylamino-group.

Preferentially, the functionalized diene elastomer (notably an SBR) maycomprise a polar function which is an alkoxysilane optionally bearing anamine group.

Preferably, this functionalized diene elastomer comprises in its mainchain at least one alkoxysilane group bonded to the elastomer chain viathe silicon atom, and optionally bearing an amine group.

Preferably, this alkoxysilane group may be represented by formula(VIII):(*—)_(a)Si(OR′)_(b)R_(c)X  (VIII)in which:

-   -   *— represents the bond to an elastomer chain;    -   the radical R represents a substituted or unsubstituted C₁-C₁₀,        or even C₁-C₈, alkyl radical, preferably a C₁-C₄ alkyl radical,        more preferentially methyl and ethyl;    -   in the alkoxy radical(s) of formula —OR′, which are optionally        partially or totally hydrolysed to hydroxyl, R′ represents a        substituted or unsubstituted C₁-C₁₀, or even C₁-C₈, alkyl        radical, preferably a C₁-C₄ alkyl radical, more preferentially        methyl and ethyl;    -   X represents a group including the other function;    -   a is equal to 1 or 2, b is equal to 1 or 2, and c is equal to 0        or 1, with the proviso that a+b+c=3.

More preferentially, the functionalized diene elastomer is a dieneelastomer (notably an SBR) comprises, within the main chain thereof, atleast one alkoxysilane group of formula (VIII) in which:

-   -   *— represents the bond to an elastomer chain;    -   the radical R represents a substituted or unsubstituted C₁-C₄        alkyl radical, more preferentially methyl and ethyl;    -   in the alkoxy radical(s) of formula —OR′, which are optionally        partially or totally hydrolysed to hydroxyl, R′ represents a        substituted or unsubstituted C₁-C₄ alkyl radical, more        preferentially methyl and ethyl;    -   X represents a group including the other function; preferably a        tertiary amine;    -   a is equal to 1 or 2, b is equal to 1 or 2, and c is equal to 0        or 1, with the proviso that a+b+c=3.

This type of elastomer is mainly obtained by functionalization of aliving elastomer derived from an anionic polymerization. It should bepointed out that it is known to those skilled in the art that when anelastomer is modified by reaction of a functionalization agent with theliving elastomer derived from a step of anionic polymerization, amixture of modified species of this elastomer is obtained, thecomposition of which depends on the modification reaction conditions andnotably on the proportion of reactive sites of the functionalizationagent relative to the number of living elastomer chains. This mixturecomprises species which are functionalized at the chain end, coupled,star-branched and/or non-functionalized.

According to a particularly preferred variant, the modified dieneelastomer comprises, as predominant species, the diene elastomerfunctionalized in the middle of the chain with an alkoxysilane groupbonded to the two branches of the diene elastomer via the silicon atom.Even more particularly, the diene elastomer functionalized in the middleof the chain with an alkoxysilane group represents 70% by weight of themodified diene elastomer. Preferably, this functionalized dieneelastomer has a glass transition temperature Tg of less than or equal to−40° C., preferably within a range extending from −110° C. to −40° C.,more preferentially from −110° C. to −60° C., even more preferentiallyfrom −110° C. to −80° C.

Whether or not they are functionalized, the diene elastomers may be usedblended (mixed) with each other. Thus, the rubber compositions inaccordance with the invention may contain just one diene elastomer,functionalized or non-functionalized, or else a mixture of several dieneelastomers, functionalized or non-functionalized, it being possible forthis (these) diene elastomer(s) to be used in combination with any typeof synthetic elastomer other than a diene elastomer, or even withpolymers other than elastomers, for example thermoplastic polymers.

Reinforcing Filler

The rubber compositions in accordance with the invention comprise atleast one reinforcing inorganic filler.

In the present patent application, the term “reinforcing inorganicfiller” should be understood, by definition, as meaning any inorganic ormineral filler (regardless of its colour and its origin, natural orsynthetic), also known as “white filler”, “clear filler” or even“non-black filler”, as opposed to carbon black, which is capable ofreinforcing by itself alone, without means other than an intermediatecoupling agent, a rubber composition intended for the manufacture oftyres, in other words capable of replacing, in its reinforcing role, aconventional tyre-grade carbon black; such a filler is generallycharacterized, in a known manner, by the presence of hydroxyl (—OH)groups at its surface.

The physical state in which the reinforcing inorganic filler is providedis not important, whether it be in the form of a powder, of micropearls,of granules, of beads or any other appropriate densified form. Needlessto say, the term “reinforcing inorganic filler” also means mixtures ofdifferent reinforcing inorganic fillers, in particular of highlydispersible siliceous and/or aluminous fillers as described below.

Mineral fillers of the siliceous type, in particular silica (SiO₂), orof the aluminous type, in particular alumina (Al₂O₃), are notablysuitable for use as reinforcing inorganic fillers. The silica used maybe any reinforcing silica known to those skilled in the art, notably anyprecipitated or fumed silica with a BET specific surface area and also aCTAB specific surface area both of less than 450 m²/g, preferably from30 to 400 m²/g. Mention will be made, as highly dispersible precipitatedsilicas (“HDSs”), for example, of the Ultrasil 7000 and Ultrasil 7005silicas from the company Evonik, the Zeosil 1165MP, 1135MP and 1115MPsilicas from the company Solvay, the Hi-Sil EZ150G silica from thecompany PPG, the Zeopol 8715, 8745 and 8755 silicas from the companyHuber or the silicas with a high specific surface area as described inpatent application WO 03/016387.

Preferably, the reinforcing inorganic filler comprises at least onesilica, and more preferentially consists of silica.

Preferably, the reinforcing inorganic filler used, in particular if itis silica, has a BET specific surface area of between 45 and 400 m²/g,more preferentially of between 60 and 300 m²/g. The BET specific surfacearea and the CTAB specific surface area are obtained according to themethods described previously.

A person skilled in the art will understand that use might be made, asfiller equivalent to the reinforcing inorganic filler described in thepresent section, of a reinforcing filler of another nature, notablyorganic nature, provided that this reinforcing filler is covered with aninorganic layer, such as silica, or else includes, at its surface,functional sites, notably hydroxyl sites, requiring the use of acoupling agent in order to establish the bond between the filler and theelastomer.

Preferably, the content of reinforcing inorganic filler in the rubbercompositions in accordance with the invention is within a rangeextending from 5 to 200 phr, more preferentially from 40 to 160 phr.

In a preferred embodiment, the rubber composition in accordance with theinvention also comprises an organic reinforcing filler, preferablycarbon black.

Organic reinforcing fillers that are notably suitable include carbonblacks or functionalized polyvinyl organic fillers, as described inpatent applications WO-A-2006/069792, WO-A-2006/069793, WO-A-2008/003434and WO-A-2008/003435.

In this embodiment, the organic reinforcing filler is carbon black. Allcarbon blacks, notably “tyre-grade” blacks, are suitable as carbonblacks. Mention will more particularly be made, among the latter, of thereinforcing carbon blacks of the 100, 200 or 300 series (ASTM grades),for instance the N115, N134, N234, N326, N330, N339, N347 or N375blacks, or else, depending on the applications targeted, the blacks ofhigher series (for example N660, N683 or N772). The carbon blacks may,for example, be already incorporated in an isoprene elastomer in theform of a masterbatch (see, for example, patent application WO 97/36724or WO 99/16600).

When it is present, the carbon black is preferentially used in a contentwithin a range extending from 0.1 to 10 phr, more preferentially from0.5 to 10 phr, notably from 1 to 4 phr.

Coupling Agent

As mentioned previously, the rubber composition in accordance with theinvention comprises at least one agent for coupling the reinforcinginorganic filler with the elastomer. This coupling agent is anorganofunctional silane comprising at least one oligomer bearing atleast one blocked mercaptosilane unit and at least one mercaptosilaneunit, the oligomer corresponding to general formula (I) below:(A)_(p)(B)_(q)   (I)in which

-   -   A is a symbol representing a blocked mercaptosilane unit        corresponding to general formula (II)

-   -   B is a symbol representing a mercaptosilane unit corresponding        to general formula (III)

-   -   -   in which formulae (II) and (III):            -   R₃ represents a group chosen from a hydrogen atom, a                linear or branched C1-C18 alkyl and a linear or branched                C2-C18 alkenyl,            -   each R₄, which may be identical or different, represents                a saturated, linear or branched C1-C6 divalent                hydrocarbon-based group,            -   each Z^(b) forms a bridging structure between a silicon                atom of one unit and a silicon atom of another unit,                these units possibly being identical or different, and                is chosen from the group consisting of (—O—)_(0.5) and                [—O(R⁰CR⁰)_(f)O—]_(0.5) with R⁰, which may be identical                or different, representing a group chosen from a                hydrogen atom, methyl, ethyl and propyl and f                representing a number within a range extending from 2 to                15,            -   each Z^(c), which may be identical or different, forms a                cyclic structure with the silicon atom of one unit and                is [—O(R⁰CR⁰)_(f)O—]_(0.5) with R⁰ and f as defined                previously,            -   each X, which may be identical or different, is chosen                from the group consisting of a hydrogen atom, a hydroxyl                group, a C1-C6 alkyl group, a C1-C6 alkoxy group and a                group) HO(R⁰CR⁰)_(f)O— with R⁰ and f as defined                previously,            -   with u+v+2w=3 in which u is a number equal to 0, 1, 2 or                3, v is a number equal to 1, 2 or 3 and w is a number                equal to 0 or 1,

    -   p is a number within a range extending from 1 to 20,

    -   q is a number within a range extending from 1 to 20.

For the purposes of the present invention, the term “organofunctionalsilane” means a molecule (or a set of molecules) which has thecharacteristic of bearing at least one mercapto group and/or one blockedmercapto group and at least one hydroxyalkoxysilyl group and/or onecyclic dialkoxysilyl group.

The term “oligomer” usually means a molecule consisting of a set ofrepeating units (also known simply as units) bonded together covalentlyforming a single chain; this molecule being smaller in size than apolymer. The term “oligomer” includes dimers, trimers, tetramers and anyother molecules containing more than four repeating units, it beingunderstood that these molecules do not constitute a polymer.

The term “mercaptosilane unit” means a repeating unit whose molecularstructure contains at least one silicon atom and a mercapto (—SH) group(also known as a thiol group) bonded to a carbon atom.

The term “blocked mercaptosilane unit” means a repeating unit whosestructure contains at least one silicon atom and at least one blockedmercapto group (also known as a blocked thiol group). A blocked mercaptogroup may be, for example, a thioester group —S—(CO)—R.

In the oligomer of general formula (I), the sequence of the blockedmercaptosilane repeating units (A) and of the mercaptosilane repeatingunits (B) is immaterial. In particular, this sequence may be alternating(for example ABABA B), in blocks (for example AA ABB B) or statistical,i.e. the sequential distribution of said units (A) and (B) obeys knownstatistical laws.

The term “bridging structure” means a chemical structure made ofcovalent bond(s) making it possible to bond two repeating unitstogether, these repeating units possibly being identical or different.

Preferably, in general formula (II), R₃ is chosen from a hydrogen atom,a linear or branched C1-C10 alkyl and a linear or branched C2-C10alkenyl.

Preferably, in general formula (II), R₃ is a linear C6-C8 alkyl.

Preferably, in general formula (II), R₃ is chosen from the groupconsisting of hexyl, heptyl and octyl.

More preferentially, in general formula (II), R₃ is heptyl (C₇H₁₅—).

Preferably, in general formulae (II) and (III), each R₄, which may beidentical or different, is a divalent hydrocarbon-based group chosenfrom the group consisting of methylene, ethylene, propylene andbutylene.

More preferentially, in general formulae (II) and (III), each R₄ isidentical and is propylene.

Preferably, in general formulae (II) and (III), Z^(b) forms a bridgingstructure between a silicon atom of one unit and another silicon atom ofanother unit, these units possibly being identical or different, and ischosen from the group consisting of (—O—)_(0.5), [—OCH₂CH₂CH₂O—]_(0.5),[—OCH₂CH₂CH₂CH₂O—]_(0.5) and [—OCH₂CH(CH₃)CH₂O—]_(0.5).

More preferentially, in general formulae (II) and (III), Z^(b) forms abridging structure between a silicon atom of one unit and anothersilicon atom of another unit, these units possibly being identical ordifferent, and is chosen from the group consisting of (—O—)_(0.5) or[—OCH₂CH(CH₃)CH₂O—]_(0.5.)

Preferably, in general formulae (II) and (III), Z^(c) forms a cyclicstructure with the silicon atom of one unit and is chosen from the groupconsisting of [—OCH₂CH₂CH₂O-]_(0.5), [—OCH₂CH₂CH₂CH₂O—]_(0.5) and[—OCH₂CH(CH₃)CH₂O—]_(0.5).

More preferentially, in general formulae (II) and (III), each Z^(c)forms a cyclic structure with the silicon atom of one unit, and is[—OCH₂CH(CH₃)CH₂O—]_(0.5).

Preferably, in general formulae (II) and (III), each X, which may beidentical or different, is chosen from the group consisting of hydroxyl,methoxy, ethoxy, methyl, ethyl, 3-hydroxypropoxy,3-hydroxy-2-methylpropoxy and 4-hydroxybut-1-oxy.

More preferentially, in general formulae (II) and (III), each X isidentical and is chosen from the group consisting of hydroxyl, methoxy,ethoxy and 3-hydroxy-2-methylpropoxy.

Preferably, in formulae (II) and (III), R₃ is heptyl (C₇H₁₅—), each R₄is propylene, Z^(b) is a bridging structure between a silicon atom ofone unit and another silicon atom of another unit and is chosen from thegroup consisting of (—O—)_(0.5) or [—OCH₂CH(CH₃)CH₂O—]_(0.5), each Z^(c)forms a cyclic structure with the silicon atom of one unit and is[—OCH₂CH(CH₃)CH₂O—]_(0.5), each X is chosen from the group consisting ofhydroxyl, methoxy, ethoxy and 3-hydroxy-2-methylpropoxy, with u+v+2w=3in which u is 0, 1, 2 or 3, v is 1, 2 or 3 and w is 0 or 1.

The notations (—O—)_(0.5) and [—O(R⁰CR⁰)_(f)O—]_(0.5) relate to half ofa siloxane bond and to half of a bridging dialkoxy group, respectively.These notations are used together with a silicon atom of the repeatingunits of the oligomer. They denote half of an oxygen atom, i.e. the halfof the oxygen atom that is bonded to the silicon atom of one repeatingunit or half of a dialkoxy group, i.e. the half of the atom of thedialkoxy group that is bonded to the silicon atom of one repeating unit;it being understood that the other half of the oxygen atom or of thedialkoxy group, respectively, is bonded to another silicon atom ofanother repeating unit of the structure of the oligomer; the repeatingunits possibly being identical or different. Thus, (—O—)_(0.5) forms asiloxane bond between two silicon atoms each belonging to a repeatingunit. [—O(R⁰CR⁰)_(f)O—]_(0.5) may form either a bridging structure (thisintermolecular structure being represented by Z^(b)) between two siliconatoms each belonging to a repeating unit, i.e. a cyclic structure (thisintramolecular structure is represented by Ze), the two oxygen atoms of[—O(R⁰CR⁰)_(f)O—]_(0.5) being bonded to the silicon atom of the unit. Aperson skilled in the art will understand that, in the oligomer offormula (I), the bridging structures may be identical or differentbetween the repeating units. For example, there may be only bridgingstructures of the type —Si—O(R⁰CR⁰)_(f)O—Si— or else a mixture ofbridging structures of the type —Si—O(R⁰CR⁰)_(f)O—Si— and of the type—Si—O—Si—.

The organofunctional silane coupling agent that may be used in thecompositions of the invention may be obtained by means of a syntheticprocess comprising at least one step (a) of transesterificationreaction:

-   -   of a diol compound of general formula (IV):        OH(R⁰CR⁰)_(f)OH   (IV)    -   in which R⁰ and f are as defined previously, i.e. R⁰, which may        be identical or different, represents a group chosen from a        hydrogen atom, methyl, ethyl and propyl, and f represents a        number ranging from 2 to 15,    -   with at least one blocked mercaptosilane compound of general        formula (V):        (RO)₃SiR₄SC(═O)R₃   (V)    -   in which R, which may be identical or different, represents a        linear C1-C6 alkyl group, R₃ and R₄ are as defined previously,        i.e. R₄ represents a saturated, linear or branched C1-C6        divalent hydrocarbon-based group; R₃ represents a group chosen        from a hydrogen atom, a linear or branched C1-C18 alkyl and a        linear or branched C2-C18 alkenyl, and    -   with at least one mercaptosilane compound of general formula        (VI):        (RO)₃SiR₄SH   (VI)

in which R and R₄ have the same definition as previously, i.e. R, whichmay be identical or different, represents a linear C1-C6 alkyl group, R₄represents a saturated, linear or branched C1-C6 divalenthydrocarbon-based group.

This transesterification reaction is well known to those skilled in theart and may be performed in the presence of a transesterificationcatalyst, for instance strong acids.

Preferentially, in the process described above, the diol compound ofgeneral formula (IV) is chosen from HOCH₂CH₂CH₂OH, HOCH₂CH₂CH₂CH₂OH andHOCH₂CH(CH₃)CH₂OH.

More preferentially, in the process described above, the diol compoundof general formula (IV) is HOCH₂CH(CH₃)CH₂OH.

Preferentially, the compounds of general formulae (V) and (VI) used inthe implementation of the process described above are those in which thegroup R is chosen from methyl, ethyl, propyl, isopropyl, n-butyl andisobutyl.

Preferentially, the compounds of general formula (V) used in theimplementation of the process described above are those in which R₃represents a group chosen from a hydrogen atom, a linear or branchedC1-C10 alkyl and a linear or branched C2-C10 alkenyl.

More preferentially, the compounds of general formula (V) used in theimplementation of the process described above are those in which R₃ is alinear C6-C8 alkyl.

Even more preferentially, the compounds of general formula (V) used inthe implementation of the process described above are those in which R₃is chosen from the group consisting of hexyl, heptyl and octyl.

More preferentially, the compounds of general formula (V) used in theimplementation of the process described above are those in which R₃ isheptyl (C₇H₁₅—).

Preferably, the compounds of general formulae (V) and (VI) used in theimplementation of the process described above are those in which R₄,which may be identical or different, is a divalent hydrocarbon-basedgroup chosen from the group consisting of methylene, ethylene, propyleneand butylene.

More preferentially, the compounds of general formulae (V) and (VI) usedin the implementation of the process described above are those in whichR₄ is identical and is propylene.

Preferentially, the compounds of general formulae (V) and (VI) used inthe implementation of the process described above are those in which R₃is heptyl, R₄ is propylene, R, which may be identical or different(preferably identical) is chosen from methyl, ethyl, propyl, isopropyl,n-butyl and isobutyl and the compound of formula (IV) used in theimplementation of the process described above is HOCH₂CH(CH₃)CH₂OH.

Mixtures of monomers (compounds of general formula (V) and compounds ofgeneral formula (VI)) may be used for synthesizing the organofunctionalsilane that may be used in the compositions of the invention.

Preferentially, the process for synthesizing the organofunctional silanecoupling agent may comprise, in addition:

-   -   at least one step (b) of treating the products obtained in        step (a) to convert some of the blocked mercapto groups, if        present in the products obtained in step (a), into free mercapto        groups (—SH) and/or    -   at least one step (c) of treating the products obtained in        step (a) to convert some of the mercapto groups, if present in        the products obtained in step (a), into blocked mercapto groups        and/or    -   at least one step (d) of partial hydrolysis of the products        obtained in step (a), of the products obtained in step (b) if        this step is performed in the process, and of the products        obtained in step (c) if this step is performed in the process.

The treatment step (b) may be, for example, a step in which a strongbase is used, for example NaOEt, to remove the blocked mercapto groupsborne by the products obtained in step (a) and to obtain free mercaptogroups borne by the products obtained in step (a).

The treatment step (c) may be, for example, a step of esterification ofthe free mercapto groups by the products obtained in step (a) using acarboxylic acid (notably C₇H₁₅COOH) or an acyl chloride (notablyC₇H₁₅COCl) to obtain blocked mercapto groups borne by the productsobtained in step (a).

The partial hydrolysis step (d) may be present when there is an excessof water relative to the products and reagents used in step (a) andoptionally steps (b) and (c), if present. The partial hydrolysis stepmakes it possible to obtain the compounds described above in whichZ^(b)═(—O—)_(0.5) and/or X═OH.

A person skilled in the art can refer notably to WO 2007/098120 A2,which describes the process for producing the organofunctional silanecoupling agent that may be used in the rubber compositions of theinvention.

Preferentially, the organofunctional silane coupling agent that may beused in the present invention may comprise other organofunctionalsilanes in addition to the oligomer of formula (I), these silanes beingreaction products obtained by performing the synthetic process describedabove.

For example, the organofunctional silane coupling agent may comprise, inaddition, at least:

-   -   i. one compound derived from general formula (II) in which R₃,        R₄, Z^(c) _(w) and X_(u) have the same definition as in        formula (II) and in which the group Z^(b) _(v) is replaced with        a group Z^(a) _(t) with Z^(a) having the same definition as the        group X, u+t+2w=3 with t being a number equal to 0, 1, 2 or 3        and u and w having the same definition as in formula (II),    -   ii. one compound derived from general formula (III) in which R₃,        R₄, Z^(c) _(w) and X_(u) have the same definition as in        formula (III) and in which the group Z^(b) _(v) is replaced with        a group Z^(a) _(t) with Z^(a) having the same definition as the        group X, u+t+2w=3 with t being a number equal to 0, 1, 2 or 3        and u and w having the same definition as in formula (III),    -   iii. one dimer consisting of two blocked mercaptosilane units of        formula (II),    -   iv. one dimer consisting of two mercaptosilane units of formula        (III),    -   v. one dimer consisting of a blocked mercaptosilane unit (II)        and a mercaptosilane unit of formula (III),    -   vi. one oligomer consisting of blocked mercaptosilane units of        formula (II),    -   vii. one oligomer consisting of mercaptosilane units of formula        (III).

Preferentially, the organofunctional silane (which may notably beobtained via the abovementioned process) has a molar percentage ofblocked mercaptosilane units that is within a range extending from 20%to 80%, preferably from 40% to 60%.

Preferentially, the organofunctional silane (which may notably beobtained via the abovementioned process) has a molar percentage ofmercaptosilane units that is within a range extending from 20% to 80%,preferably from 40% to 60%.

More preferentially, the organofunctional silane (which may notably beobtained via the abovementioned process) has a molar percentage ofblocked mercaptosilane units that is within a range extending from 50%to 55% and the organofunctional silane (which may notably be obtainedvia the abovementioned process) has a molar percentage of mercaptosilaneunits that is within a range extending from 45% to 50%.

The molar percentage of blocked mercaptosilane units and the molarpercentage of mercaptosilane units in the organofunctional silane thatmay be used in the compositions of the invention may be determined viaany method that is well known to those skilled in the art, for instance¹H NMR.

The organofunctional silane coupling agent that may be used in therubber compositions of the invention is commercially available fromMomentive. Inc. under the commercial reference NXT-Z45.

In one variant of the invention, the coupling agent that may be used inthe compositions of the invention may predominantly comprise anorganofunctional silane as described above and a second coupling agent,of chemical structure different from this organofunctional silane. Thissecond coupling agent may be, for example, a polysulfide silane.

Preferentially, in this embodiment, the coupling agent that may be usedin the compositions of the invention comprises at least 70% by weight ofan organofunctional silane as described above relative to the totalweight of the coupling agents used and a second coupling agent ofchemical structure different from this organofunctional silane; thissecond coupling agent notably being present in a content of not morethan 30% by weight relative to the total weight of the coupling agentsused. This second coupling agent may be, for example, a polysulfidesilane.

Polysulfide silanes are well known to those skilled in the art and areused as agent for coupling a reinforcing inorganic filler withelastomers in rubber compositions.

The polysulfide silanes may be “symmetrical” or “asymmetrical” dependingon their particular structure. Such compounds are described, forexample, in patent applications WO 03/002648 (or US 2005/016651) and WO03/002649 (or US 2005/016650).

Agents that are suitable in particular, without the definition belowbeing limiting, are “symmetrical” polysulfide silanes, corresponding togeneral formula (VII) below:Z-D-Sx-D-Z   (VII)in which:

-   -   x is an integer from 2 to 8 (preferably from 2 to 5);    -   the symbols D, which may be identical or different, represent a        divalent hydrocarbon-based radical (preferably C₁-C₁₈ alkylene        groups or C₆-C₁₂ arylene groups, more particularly C₁-C₁₀ and        notably C₁-C₄ alkylenes, in particular propylene);    -   the symbols Z, which may be identical or different, correspond        to one of the formulae below:

in which:

-   -   the radicals R^(a), which may be substituted or unsubstituted        and identical to or different from each other, represent a        C₁-C₁₈ alkyl, a C₅-C₁₈ cycloalkyl or a C₆-C₁₈ aryl (preferably a        C₁-C₆ alkyl, a cyclohexyl or a phenyl, notably a C₁-C₄ alkyl,        more particularly methyl and/or ethyl),    -   the radicals R^(b), which may be substituted or unsubstituted        and identical to or different from each other, represent a        C₁-C₁₈ alkoxyl or a C₅-C₁₈ cycloalkoxyl group (preferably a        group selected from C₁-C₈ alkoxyls and C₅-C₈ cycloalkoxyls, even        more preferentially a group chosen from C₁-C₄ alkoxyls, in        particular methoxyl and ethoxyl).

In the case of a mixture of polysulfide alkoxysilanes corresponding tothe above formula (VII), notably normal commercially available mixtures,the mean value of the “x” indices is a fractional number preferablybetween 2 and 5, more preferentially close to 4. However, the inventionmay also be advantageously performed, for example, with alkoxysilanedisulfides (x=2).

As examples of polysulfide silanes, mention will be made moreparticularly of bis((C₁-C₄)alkoxyl(C₁-C₄)alkylsilyl(C₁-C₄)alkyl)polysulfides (notably disulfides, trisulfides or tetrasulfides), forinstance bis(3-trimethoxysilylpropyl) or bis(3-triethoxysilylpropyl)polysulfides. Among these compounds, use is made in particular ofbis(3-triethoxysilylpropyl) tetrasulfide, abbreviated to TESPT, offormula [(C₂H₅O)₃Si(CH₂)₃S₂]₂, or bis(3-triethoxysilylpropyl) disulfide,abbreviated to TESPD, of formula [(C₂H₅O)₃Si(CH₂)₃S]₂. Preferentialexamples that will also be mentioned includebis(mono(C₁-C₄)alkoxyldi(C₁-C₄)alkylsilylpropyl) polysulfides (notablydisulfides, trisulfides or tetrasulfides), more particularlybis(monoethoxydimethylsilylpropyl) tetrasulfide, as described in patentapplication WO 02/083782 (or US 2004/132880).

Preferentially, the coupling agent used in the compositions of theinvention consists of an organofunctional silane comprising at least oneoligomer of general formula (I) as described above or a mixture oforganofunctional silanes as described above.

In the rubber compositions in accordance with the invention, the contentof coupling agent is preferentially within a range extending from 1 to20 phr, from 1 to 15 phr and more preferentially from 3 to 14 phr.

These rubber compositions of the invention may also optionally contain,in addition to the abovementioned coupling agents, coupling activators,agents for covering the inorganic fillers or more generally processingaids that are capable, in a known manner, by means of improving thedispersion of the filler in the rubber matrix and of lowering theviscosity of the compositions, of improving their ability to beprocessed in the raw state, these agents being, for example,hydrolysable silanes such as alkylalkoxysilanes, polyols, fatty acids,polyethers, primary, secondary or tertiary amines, or hydroxylated orhydrolysable polyorganosiloxanes.

Hydrocarbon-Based Resin

The compositions of the invention comprise at least one specifichydrocarbon-based resin.

This hydrocarbon-based resin is predominantly composed of monomerschosen from the group consisting of cyclopentadiene, dicyclopentadiene,methylcyclopentadiene, and mixtures of these monomers. This resin mayoptionally be hydrogenated.

The hydrocarbon-based resin is preferably a plasticizinghydrocarbon-based resin.

In a manner known to those skilled in the art, the term “plasticizingresin” is reserved in the present patent application, by definition, fora compound which is, on the one hand, solid at room temperature (23° C.)(as opposed to a liquid plasticizing compound such as an oil) and, onthe other hand, compatible (that is to say miscible at the content used,typically of greater than 5 phr) with the rubber composition for whichit is intended, so as to act as a true diluent.

Hydrocarbon-based resins are polymers that are well known to thoseskilled in the art, which are miscible by nature in diene elastomercompositions, when they are also described as “plasticizing”. They havebeen described, for example, in the book entitled “Hydrocarbon Resins”by R. Mildenberg, M. Zander and G. Collin (New York, V C H, 1997, ISBN3-527-28617-9), Chapter 5 of which is devoted to their applications,notably in the tyre rubber field (5.5. “Rubber Tires and MechanicalGoods”). They may be aliphatic, aromatic or of the aliphatic/aromatictype, i.e. based on aliphatic and/or aromatic monomers. They may benatural or synthetic and may or may not be petroleum-based (if such isthe case, they are also known under as petroleum resins). They arepreferentially exclusively hydrocarbon-based, i.e. they include onlycarbon and hydrogen atoms.

The Applicant has discovered that, among plasticized hydrocarbon-basedresins, resins predominantly composed of monomers chosen from the groupconsisting of cyclopentadiene, dicyclopentadiene, methylcyclopentadieneand mixtures of these monomers used in combination with theorganofunctional silane coupling agent as described previously make itpossible, surprisingly, to obtain rubber compositions whose rollingresistance is improved without the wet grip being penalized. Thesecompositions also have the advantage of having improved grip onsnow-covered ground.

When reference is made to a “predominant monomer” in a hydrocarbon-basedresin, this is understood to mean, within the meaning of the presentinvention, that this monomer is predominant among the monomers formingthe resin, that is to say that it is the one which represents thelargest mass fraction among the monomers forming the resin. Thus, forexample, a hydrocarbon-based resin predominantly composed ofcyclopentadiene monomers is a resin in which the cyclopentadienemonomers represent the largest amount by mass among all the monomersmaking up this hydrocarbon-based resin. Similarly, a hydrocarbon-basedresin predominantly composed of monomers chosen from the groupconsisting of cyclopentadiene, dicyclopentadiene, methylcyclopentadieneand mixtures of these monomers is a hydrocarbon-based resin in which thesum of the monomers chosen from the group consisting of cyclopentadiene,dicyclopentadiene, methylcyclopentadiene and mixtures of these monomersrepresents the largest amount by mass among all the monomers making upsaid resin. In other words, a “predominant monomer” is a monomer whichrepresents the largest mass fraction in the resin. On the contrary, a“minor monomer” is a monomer which does not represent the largest massfraction in the resin.

Preferentially, the optionally hydrogenated hydrocarbon-based resincomprises at least 50% by mass (>50% by mass) of monomers chosen fromthe group consisting of cyclopentadiene, dicyclopentadiene,methylcyclopentadiene, and mixtures of these monomers, relative to thetotal mass of all of the monomers of which said resin is constituted.

Preferably, the optionally hydrogenated hydrocarbon-based resin may alsocomprise, in minor amount, aromatic monomers and/or aliphatic monomers.

Preferentially, the optionally hydrogenated hydrocarbon-based resincomprises not more than 50% by mass (<50% by mass) of aromatic monomersand/or aliphatic monomers relative to the total mass of all of themonomers of which said resin is constituted, and more preferentiallycomprises not more than 40% by mass (<40% by mass) of aromatic monomersand/or aliphatic monomers.

Examples of aromatic monomers that may be mentioned include monomerschosen from the group consisting of styrene, α-methylstyrene, ortho-,meta- or para-methylstyrene, vinyltoluene, para-(tert-butyl)styrene,methoxystyrenes, chlorostyrenes, vinylmesitylene, divinylbenzene,vinylnaphthalene, indene, or any vinylaromatic monomer derived from a C9fraction (or more generally from a C8, C9 or C10 fraction). Preferably,the vinylaromatic monomer is styrene or a vinylaromatic monomer derivedfrom a C9 fraction.

Examples of aliphatic monomers that may be mentioned include monomerschosen from the group consisting of isoprene, piperylene and amylene.

According to a preferred embodiment, the optionally hydrogenatedhydrocarbon-based resin is chosen from the group consisting ofcyclopentadiene homopolymer resins, dicyclopentadiene homopolymerresins, methylcyclopentadiene homopolymer resins, and mixtures of theseabovementioned homopolymer resins.

Also in a preferred embodiment, the optionally hydrogenatedhydrocarbon-based resin may be a mixture of abovementioned homopolymerresins and abovementioned copolymer resins.

According to another embodiment which is also very preferential, theoptionally hydrogenated hydrocarbon-based resin is chosen from the groupconsisting of resins predominantly composed of monomers chosen from thegroup consisting of cyclopentadiene, dicyclopentadiene,methylcyclopentadiene and mixtures of these monomers and in minor amountcomposed of aromatic monomers.

The optionally hydrogenated hydrocarbon-based resins that may be used inthe compositions of the invention are often called CPD resins or DCPDresins.

The optionally hydrogenated hydrocarbon-based resins are obtained viaprocesses that are well known to those skilled in the art, for instanceby thermal polymerization (i.e. without a polymerization catalyst).

Preferably, the optionally hydrogenated hydrocarbon-based resin has anumber-average molecular mass Mn within a range extending from 200 to2000 g/mol, preferably from 200 to 600 g/mol.

Preferably, the optionally hydrogenated hydrocarbon-based resin has apolydispersity index PI of less than or equal to 2, preferably less thanor equal to 1.8, preferably less than 1.7.

Preferably, the optionally hydrogenated hydrocarbon-based resin has aglass transition temperature Tg of greater than or equal to 30° C.,preferably within a range extending from 30° C. to 80° C.

Preferably, the optionally hydrogenated hydrocarbon-based resin is alsocomposed in minor amount of aromatic monomers.

Preferably, the content of aromatic protons in the optionallyhydrogenated hydrocarbon-based resin is within a range extending from 1%to 20%, preferably from 2% to 15% and even more preferentially from 2%to 10%.

Preferably, the optionally hydrogenated hydrocarbon-based resin has anumber-average molecular mass Mn within a range extending from 200 to600 g/mol and a polydispersity index PI of less than or equal to 2,preferably less than or equal to 1.8, preferably less than 1.7.

Preferentially, the content of optionally hydrogenated hydrocarbon-basedresin is within a range extending from 15 phr to 150 phr, preferentiallyfrom 25 to 120 phr and more preferentially from 30 to 115 phr. This isbecause, below 15 phr of the hydrocarbon-based resin that is of use forthe purposes of the invention, the effect of the resin would beinsufficient and the composition might present grip problems, while,above 150 phr, the composition might exhibit a difficulty inmanufacturing in order to readily incorporate all of said resin into thecomposition.

The glass transition temperature, the softening point, themacrostructure (Mn, Mw, PI) and the content of aromatic protons of theoptionally hydrogenated hydrocarbon-based resin are determined accordingto the methods described above.

The optionally hydrogenated hydrocarbon-based resins, predominantlycomposed of monomers chosen from the group consisting ofcyclopentadiene, dicyclopentadiene, methylcyclopentadiene, and mixturesof these monomers, are commercially available from suppliers such asExxonMobil, notably under the references Escorez E5600, Escorez E5415,Escorez E5320 and PR-383.

Crosslinking System

In the compositions of the invention, use may be made of any type ofcrosslinking system known to those skilled in the art for rubbercompositions.

Preferably, the crosslinking system is a vulcanization system, i.e. asystem based on sulfur (or on a sulfur-donating agent) and on a primaryvulcanization accelerator. Various known secondary vulcanizationaccelerators or vulcanization activators, such as zinc oxide, stearicacid or equivalent compounds, or guanidine derivatives (in particulardiphenylguanidine), are added to this base vulcanization system, beingincorporated during the non-productive first phase and/or during theproductive phase, as described subsequently.

The sulfur is used in a preferential content within a range extendingfrom 0.3 to 10 phr, more preferentially from 0.3 to 5 phr, in particularfrom 0.3 to 3 phr.

The vulcanization system of the compositions of the invention may alsocomprise one or more additional accelerators, for example compounds ofthe thiuram, zinc dithiocarbamate, sulfenamide, guanidine orthiophosphate family. Use may be made in particular of any compound thatis capable of acting as accelerator of the vulcanization of dieneelastomers in the presence of sulfur, notably accelerators of thethiazole type and derivatives thereof, and accelerators of thiuram orzinc dithiocarbamate type. These accelerators are more preferentiallychosen from the group consisting of 2-mercaptobenzothiazyl disulfide(abbreviated to “MBTS”), N-cyclohexyl-2-benzothiazolesulfenamide(abbreviated to “CBS”), N,N-dicyclohexyl-2-benzothiazolesulfenamide(abbreviated to “DCBS”), N-(tert-butyl)-2-benzothiazolesulfenamide(abbreviated to “TBBS”), N-(tert-butyl)-2-benzothiazolesulfenimide(abbreviated to “TBSI”), zinc dibenzyldithiocarbamate (abbreviated to“ZBEC”), tetrabenzylthiuram disulfide (TBzTD), and mixtures of thesecompounds. Preferably, use is made of a primary accelerator of thesulfenamide type.

Other Possible Additives

The rubber compositions according to the invention as describedpreviously make it possible, by themselves alone, to address the posedtechnical problem; in particular, they make it possible to haveexcellent rolling resistance properties without penalizing the wet grip.However, they may optionally also include all or some of the customaryadditives usually used in elastomer compositions intended notably forthe manufacture of semi-finished products for tyres or of rubberarticles, for instance pigments, protective agents such as antiozonewaxes, chemical antiozonants, antioxidants, plasticizers other thanthose described previously, anti-fatigue agents, reinforcing resins,methylene acceptors (for example novolac phenolic resin) or methylenedonors (for example HMT or H3M).

The composition according to the invention may also include aplasticizing system. This plasticizing system may be composed of ahydrocarbon-based resin with a Tg of greater than 20° C. other than aDCDP resin, in addition to the specific hydrocarbon-based resindescribed previously, and/or a plasticizing oil.

Needless to say, the compositions in accordance with the invention maybe used alone or as a blend (i.e., as a mixture) with any other rubbercomposition that may be used for the manufacture of rubber articles,notably of semi-finished articles for tyres, or of tyres.

It goes without saying that the invention relates to the rubbercompositions described previously both in the “raw” or non-crosslinkedstate (i.e., before curing) and in the “cured” or crosslinked, or alsovulcanized, state (i.e., after crosslinking or vulcanization).

2.2—Preparation of the Rubber Compositions

The rubber compositions in accordance with the invention aremanufactured in suitable mixers, using two successive preparation phasesthat are well known to those skilled in the art: a first phase ofthermomechanical working or kneading (sometimes termed the“non-productive” phase) at high temperature, up to a maximum temperatureof between 110° C. and 200° C., preferably between 130° C. and 180° C.,followed by a second phase of mechanical working (sometimes termed the“productive” phase) at a lower temperature, typically of less than 110°C., for example between 60° C. and 100° C., during which finishing phasethe crosslinking or vulcanization system is incorporated. Such phaseshave been described, for example, in patent applications EP-A-0501227,EP-A-0735088, EP-A-0810258, WO00/05300 or WO00/05301.

The first (non-productive) phase is preferentially performed in severalthermomechanical steps. During a first step, the elastomers, thereinforcing fillers, notably the reinforcing inorganic filler, theorganofunctional silane coupling agent as described above, the specifichydrocarbon-based resin as described above (and optionally the otheringredients with the exception of the crosslinking system) areintroduced into a suitable mixer, such as a customary internal mixer, ata temperature between 20° C. and 100° C. and preferably between 25° C.and 100° C. After a few minutes, preferentially from 0.5 to 2 min, and arise in the temperature to 90° C. or to 100° C., the other ingredients(i.e. those which remain, if not all were put in at the start) are addedall at once or in portions, with the exception of the crosslinkingsystem, during a mixing ranging from 20 seconds to a few minutes. Thetotal duration of the kneading, in this non-productive phase, ispreferably between 2 and 10 minutes at a temperature of less than orequal to 180° C. and preferentially of less than or equal to 170° C.

After cooling of the mixture thus obtained, the crosslinking system isthen incorporated at low temperature (typically less than 100° C.),generally in an external mixer, such as an open mill; the whole is thenmixed (productive phase) for a few minutes, for example between 5 and 15min.

The final composition thus obtained is subsequently calendered, forexample in the form of a sheet or of a plaque, notably for laboratorycharacterization, or else extruded, in order to form, for example, arubber profile used in the manufacture of semi-finished products fortyres. These products may then be used for the manufacture of tyres,according to techniques known to those skilled in the art.

The crosslinking (or curing) is performed in a known manner at atemperature generally of between 130° C. and 200° C., under pressure,for a sufficient time which may range, for example, between 5 and 90min, as a function notably of the curing temperature, of thevulcanization system adopted, of the kinetics of crosslinking of thecomposition under consideration or else of the size of the tyre.

2.3—Semi-Finished Products for a Tyre and Tyre

Another subject of the present invention relates to a semi-finishedarticle for a tyre, comprising at least one rubber composition inaccordance with the invention and as defined above. The semi-finishedarticles of the present invention have improved rolling resistanceproperties without the wet grip being penalized. Advantageously, theyalso have improved grip on snow-covered ground.

The semi-finished article may be any article of use for the manufactureof a finished rubber article such as a tyre.

Preferentially, the semi-finished article for a tyre may be chosen fromunderlayers, bonding rubbers between rubbers of different natures orcalendering rubbers for metal or textile reinforcers, sidewall rubbersand treads. More preferentially, the semi-finished article for a tyre isa tread. The semi-finished articles are obtained via methods that arewell known to those skilled in the art.

Another subject of the present invention relates to a tyre comprising atleast one rubber composition in accordance with the invention and asdescribed above or comprising at least one semi-finished article for atyre as described above. The tyres of the present invention haveimproved rolling resistance properties without the wet grip beingpenalized. Advantageously, they also have grip on snow-covered ground.The tyres of the invention may notably be intended to equip motorvehicles of the passenger vehicle, SUV (“Sports Utility Vehicles”),two-wheel vehicle (notably motorcycle) or aircraft type, such asindustrial vehicles chosen from vans, heavy-duty vehicles, i.e.underground trains, buses, heavy road transport vehicles (lorries,tractors, trailers) or off-road vehicles such as heavy agricultural orconstruction plant vehicles, and other transportation or handlingvehicles. The tyres of the invention are obtained via methods that arewell known to those skilled in the art.

3—EXAMPLES

The examples that follow illustrate the invention without, however,limiting it.

3.1—Manufacture of the Rubber Compositions:

For the following tests, the compositions are prepared in the followingway: the diene elastomers, the reinforcing inorganic filler (silica),the carbon black, the coupling agent to be tested and then, afterkneading for one to two minutes, the various other ingredients,including the resin to be tested, with the exception of thevulcanization system, are introduced into an internal mixer which is 70%filled and which has an initial vessel temperature of about 50° C.Thermomechanical working (non-productive phase) is then performed in onestep (total kneading time equal to about 5 min), until a maximum“dropping” temperature of about 165° C. is reached.

The mixture thus obtained is recovered and cooled and the vulcanizationsystem (sulfur and accelerator) is then added on an external mixer(homofinisher) at 70° C., the whole being mixed (productive phase) forabout 5 to 6 min.

The compositions thus obtained are then calendered, either in the formof plaques (thickness of 2 to 3 mm) or of thin sheets of rubber formeasurement of their physical or mechanical properties after curing.

3.2—Test A:

The aim of this test is to demonstrate the improved rolling resistanceproperties of a rubber composition in accordance with the invention whencompared with rubber compositions not in accordance using plasticizingresins other than hydrocarbon-based resins predominantly composed ofmonomers chosen from the group consisting of cyclopentadiene,dicyclopentadiene, methylcyclopentadiene, and mixtures of thesemonomers, and using a coupling agent other than the organofunctionalsilane comprising an oligomer of formula (I).

In the rest of the description, for the sake of simplicity, thehydrocarbon-based resins predominantly composed of monomers chosen fromthe group consisting of cyclopentadiene, dicyclopentadiene,methylcyclopentadiene, and mixtures of these monomers, will be referredto as DCDP resins. The organofunctional silane coupling agent comprisingan oligomer of formula (I) will be called the mercapto/blocked mercaptoorganofunctional silane coupling agent.

Eight rubber compositions based on diene elastomer reinforced withsilica are compared, these compositions differing from each otheressentially in the characteristics that follow:

-   -   composition CP1 is a non-conforming rubber composition        comprising a resin based on α-methylstyrene and/or styrene and a        polysulfide silane coupling agent,    -   composition CP2 is a non-conforming rubber composition        comprising a resin based on α-methylstyrene and/or styrene and        the mercapto/blocked mercapto organofunctional silane coupling        agent,    -   composition CP3 is a non-conforming rubber composition        comprising a resin based on terpenes (β-pinene) and a        polysulfide silane coupling agent,    -   composition CP4 is a non-conforming rubber composition        comprising a resin based on terpenes (β-pinene) and the        mercapto/blocked mercapto organofunctional silane coupling        agent,    -   composition CP5 is a non-conforming rubber composition        comprising an aromatic resin based on coumarone-indene and a        polysulfide silane coupling agent,    -   composition CP6 is a non-conforming rubber composition        comprising a resin based on coumarone-indene and the        mercapto/blocked mercapto organofunctional silane coupling        agent,    -   composition CP7 is a non-conforming rubber composition        comprising a DCPD resin and a polysulfide silane coupling agent,    -   composition CP8 is a conforming rubber composition comprising a        DCPD resin and the mercapto/blocked mercapto organofunctional        silane coupling agent.

Table I presents the formulations of the rubber compositions CP1 to CP8.The content of the various ingredients is expressed in phr.

TABLE I CP1 CP2 CP3 CP4 CP5 CP6 CP7 CP8 Elastomer (1) 100 100 100 100100 100 100 100 Reinforcing 130 130 130 130 130 130 130 130 inorganicfiller (2) Coupling agent (3) 11 (—) 11 (—) 11 (—) 11 (—) Coupling agent(4) (—) 11 (—) 11 (—) 11 (—) 11 Resin 1 (5) 88 88 (—) (—) (—) (—) (—)(—) Resin 2 (5) (—) (—) 88 88 (—) (—) (—) (—) Resin 3 (5) (—) (—) (—)(—) 88 88 (−) (−) Resin 4 (5) (—) (—) (—) (—) (—) (—) 88 88 Carbon black(6) 4 4 4 4 4 4 4 4 Antioxidant (7) 6 6 6 6 6 6 6 6 Anti-ozone wax 2.852.85 2.85 2.85 2.85 2.85 2.85 2.85 DPG (8) 2.4 2.4 2.4 2.4 2.4 2.4 2.42.4 Stearic acid (9) 3 3 3 3 3 3 3 3 ZnO (10) 0.9 0.9 0.9 0.9 0.9 0.90.9 0.9 Accelerator (11) 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 Soluble sulfur0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 (1) Styrene-butadiene copolymer,aminoalkoxysilane-functional in the middle of the chain, with a glasstransition temperature equal to −88° C., the microstructure of thiscopolymer is determined via the NIR method. The content of 1,2- units is12.7% relative to the butadiene units. The mass content of styrene is2.1%; this copolymer is synthesized according to the process describedin WO 2017/060395; (2) Zeosil 1165 MP silica from the company Solvay, ofHDS type; its BET specific surface area is 160 m²/g; (3)bis(triethoxysilylpropyl)tetrasulfide polysulfide silane coupling agentsold under the reference Si69 from the company Evonik-Degussa; (4)Mercapto/blocked mercapto organofunctional silane coupling agent soldunder the reference NXT-Z45 by Momentive Inc.; (5) Resins 1 to 4: seetable II below; (6) ASTM N234 grade carbon black sold by Cabot; (7)N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine (Santoflex 6-PPD)from the company Flexsys and 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ);(8) Diphenylguanidine, Perkacit DPG from the company Flexsys; (9)Pristerene 4931 stearin from the company Uniqema; (10) Zinc oxide,industrial grade - from Umicore; (11)N-Cyclohexyl-2-benzothiazolesulfenamide (Santocure CBS from the companyFlexsys).

The resins used in compositions CP1 to CP8 are presented in Table 2below.

TABLE II Softening Content of Commercial Resin Chemical point Tg Mn Mwaromatic Resin name manufacturer nature (° C.) (° C.) g/mol g/mol PIprotons Resin 1 Kristalex Eastman α- 83 37 656 1147 1.75 52 F85 ChemicalMethylstyrene and styrene Resin 2 Piccolyte Pinova Terpenes 135 87 12452368 1.9 4 S135 (β-pinene) Resin 3 Neopolymer Nisseki Coumarone- 98 48735 1164 1.72 38 L-90 indene aromatic Resin 4 PR-383 ExxonMobil DCDP 10051 490 805 1.65 10 The resins were analysed via the methods described inparagraph 1 ″Measuring methods used″.

Table III gives the properties after curing, about 40 min at 150° C. ofcompositions CP1 to CP8.

TABLE III CP1 CP2 CP3 CP4 CP5 CP6 CP7 CP8 Tan (δ)_(max) 100 95 122 116110 119 79 68 at 23° C. (base 100) Tan (δ)_(−20° C.) 100 90 58 53 92 72149 140 (base 100) G*_(−20° C.) 100 105 171 185 122 137 74 69 (in base100)

Examination of table III shows that, among all the compositionscomprising a polysulfide silane coupling agent (compositions CP3 and CP5not in accordance with the invention), only composition CP7 not inaccordance with the invention and comprising the resin DCPD makes itpossible to improve the rolling resistance and also the wet grip and thegrip on snow-covered ground, relative to the control composition CP1.

It is also observed that, among all the compositions comprising amercapto/blocked mercapto organofunctional silane coupling agent(compositions CP2, CP4 and CP6 not in accordance), only composition CP8in accordance with the invention and comprising the resin DCPD makes itpossible to improve the rolling resistance and also the wet grip and thegrip on snow-covered ground, relative to the control composition CP1.

Furthermore, surprisingly, it is found that composition CP8 inaccordance with the invention combining the presence of themercapto/blocked mercapto organofunctional silane coupling agent and theDCPD resin shows an improvement in the rolling resistance performance(improvement of −32) and in the grip on snow-covered ground (improvementof −31) which is greater than the addition of the effects of the rollingresistance and of the grip effect on snow-covered ground of compositionCP2 relative to composition CP1 (rolling resistance: −5 and grip onsnow-covered ground: +5) and that of composition CP7 relative to CP1(rolling resistance: −21 and grip on snow-covered ground: −26). Truesynergism is thus seen on the effect of the choice of themercapto/blocked mercapto organofunctional silane coupling agent and ofthe resin DCDP within the same composition for the two abovementionedproperties.

It is furthermore also noted, surprisingly, that composition CP8 inaccordance with the invention has improved rolling resistance propertiesand grip properties on snow-covered ground with respect to all of thecompositions and in particular with respect to composition CP7 not inaccordance with the invention without the wet grip being penalized.Specifically, it is found that composition CP8 in accordance with theinvention has improved wet grip performance relative to the othernon-conforming compositions, and also relative to the controlcomposition CP1.

The invention claimed is:
 1. A rubber composition based on at least: adiene elastomer; a reinforcing inorganic filler; an agent for couplingthe reinforcing inorganic filler with the diene elastomer, the couplingagent being an organofunctional silane comprising at least one oligomerbearing at least one blocked mercaptosilane unit and at least onemercaptosilane unit, the at least one oligomer corresponding to generalformula (I) below:(A)_(p)(B)_(q)  (I) in which A is a blocked mercaptosilane unitcorresponding to general formula (II)

B is a mercaptosilane unit corresponding to general formula (III)

in which formulae (II) and (III): R₃ is selected from the groupconsisting of a hydrogen atom, a linear or branched C1-C18 alkyl and alinear or branched C2-C18 alkenyl, each R₄, which may be identical ordifferent, is a saturated, linear or branched C1-C6 divalenthydrocarbon-based group, Z^(b) forms a bridging structure between asilicon atom of one unit and a silicon atom of another unit, these unitsbeing identical or different, and is selected from the group consistingof (—O—)_(0.5) and [—O(R⁰CR⁰)_(f)O—]_(0.5) with R⁰, which may beidentical or different, being a group selected from the group consistingof a hydrogen atom, methyl, ethyl and propyl and f being a number withina range extending from 2 to 15, each Z^(c), which may be identical ordifferent, forms a cyclic structure with the silicon atom of one unitand is [—O(R⁰CR⁰)_(f)O—]_(0.5) with R⁰ and f as defined above, each X,which may be identical or different, is selected from the groupconsisting of a hydrogen atom, a hydroxyl group, a C1-C6 alkyl group, aC1-C6 alkoxy group and a group)HO(R⁰CR⁰)_(f)O— with R⁰ and f as definedabove, and with u+v+2w=3 in which u is a number equal to 0, 1, 2 or 3, vis a number equal to 1, 2 or 3 and w is a number equal to 0 or 1, p is anumber within a range extending from 1 to 20, and q is a number within arange extending from 1 to 20; a hydrocarbon-based resin predominantlycomposed of monomers selected from the group consisting ofcyclopentadiene, dicyclopentadiene, methylcyclopentadiene and mixturesthereof; and a crosslinking system.
 2. The rubber composition accordingto claim 1, wherein R₃ is selected from the group consisting of ahydrogen atom, a linear or branched C1-C10 alkyl and a linear orbranched C2-C10 alkenyl.
 3. The rubber composition according to claim 1,wherein R₄ of formulae (II) and (III), which may be identical ordifferent, is a divalent hydrocarbon-based group selected from the groupconsisting of methylene, ethylene, propylene and butylene.
 4. The rubbercomposition according to claim 1, wherein Z^(b) is selected from thegroup consisting of (—O—)_(0.5), [—OCH₂CH₂CH₂O—]_(0.5),[—OCH₂CH₂CH₂CH₂O—]_(0.5) and [—OCH₂CH(CH₃)CH₂O—]_(0.5).
 5. The rubbercomposition according to claim 4, wherein Z^(b) is selected from thegroup consisting of (—O—)_(0.5) or [—OCH₂CH(CH₃)CH₂O—]_(0.5).
 6. Therubber composition according to claim 1, wherein Z^(c) is selected fromthe group consisting of [—OCH₂CH₂CH₂O—]_(0.5), [—OCH₂CH₂CH₂CH₂O—]_(0.5)and [—OCH₂CH(CH₃)CH₂O—]_(0.5).
 7. The rubber composition according toclaim 1, wherein X is selected from the group consisting of hydroxyl,methoxy, ethoxy, methyl, ethyl, 3-hydroxypropoxy,3-hydroxy-2-methylpropoxy and 4-hydroxybut-1-oxy.
 8. The rubbercomposition according to claim 1, wherein the organofunctional silanecoupling agent is able to be obtained via a synthetic process comprisinga transesterification reaction of a diol compound of general formula(IV):OH(R⁰CR⁰)_(f)OH  (IV) in which R⁰, which may be identical or different,is a group selected from a hydrogen atom, methyl, ethyl and propyl, andf is a number ranging from 2 to 15, with at least one blockedmercaptosilane compound of general formula (V):(RO)₃SiR₄SC(═O)R₃  (V) in which R, which may be identical or different,is a linear C1-C6 alkyl group, R₃ is a group selected from the groupconsisting of a hydrogen atom, a linear or branched C1-C18 alkyl and alinear or branched C2-C18 alkenyl, and R₄ is a saturated, linear orbranched C1-C6 divalent hydrocarbon-based group and with at least onemercaptosilane compound of general formula (VI):(RO)₃SiR₄SH  (VI) in which R is a linear C1-C6 alkyl group and R₄ is asaturated, linear or branched C1-C6 divalent hydrocarbon-based group. 9.The rubber composition according to claim 1, wherein thehydrocarbon-based resin has a number-average molecular mass Mn that iswithin a range extending from 200 to 2000 g/mol.
 10. The rubbercomposition according to claim 1, wherein the hydrocarbon-based resinhas a glass transition temperature of greater than or equal to 30° C.11. The rubber composition according to claim 1, wherein a content ofthe hydrocarbon-based resin is within a range extending from 15 to 150phr.
 12. The rubber composition according to claim 1, wherein a contentof reinforcing inorganic filler is within a range extending from 5 to200 phr.
 13. The rubber composition according to claim 1, wherein thereinforcing inorganic filler comprises at least one silica.
 14. Therubber composition according to claim 1 further comprising carbon black.15. The rubber composition according to claim 1, wherein the dieneelastomer is selected from the group consisting of polybutadienes,natural rubber, synthetic polyisoprenes, butadiene copolymers, isoprenecopolymers, and mixtures thereof.
 16. The rubber composition accordingto claim 15, wherein the diene elastomer is selected from the groupconsisting of polybutadienes, butadiene-styrene copolymers,isoprene-butadiene copolymers, isoprene-styrene copolymers,isoprene-butadiene-styrene copolymers, and mixtures thereof.
 17. Therubber composition according to claim 1, wherein the diene elastomer isa functionalized elastomer.
 18. The rubber composition according toclaim 17, wherein the functionalized elastomer has a glass transitiontemperature Tg of less than or equal to −40° C.
 19. A semi-finishedarticle for a tire comprising at least one rubber composition accordingto claim
 1. 20. A tire comprising at least one rubber compositionaccording to claim 1.